The invention relates generally to apparatus for substrate processing and, more particularly, to a structure allowing remote plasma clean gases to by-pass a blocker plate.
The fabrication of semiconductor products, such as integrated circuits, often involves the formation of layers on a substrate, such as a silicon wafer. Various techniques have been developed for the deposition processes, as the layers often involve different materials. For example, a metal layer might be deposited and patterned to form conductive interconnects, or a dielectric layer might be formed to electrically insulate one conductive layer from another. Some types of layer formation processes that have been used to form layers of dielectric materials and other materials are chemical vapor deposition (CVD) processes.
CVD processes include thermal deposition processes, in which precursor gases or vapors react in response to the heated surface of the substrate, as well as plasma-enhanced CVD (xe2x80x9cPECVDxe2x80x9d) processes, in which electromagnetic energy is applied to at least one precursor gas or vapor to transform the precursor into a more reactive plasma. Forming a plasma can lower the temperature required to form a film, increase the rate of formation, or both. Therefore, plasma-enhanced process are desirable in many applications.
When a layer is formed on a substrate, some material is usually also deposited on the walls of the deposition chamber and other components of the deposition system as residue. The material on the walls of the chamber is generally undesirable because the residue can build up and become a source of particulate contamination, causing wafers to be rejected. Several cleaning procedures have been developed to remove residue from inside the chamber. One type of procedure, known as a xe2x80x9cwet-cleanxe2x80x9d is performed by partially disassembling the deposition chamber and wiping the surfaces down with appropriate cleaning fluids. Other types of cleaning processes utilize a plasma to remove the residue by converting it to a volatile product that can be removed by the chamber exhaust system. These processes are known as xe2x80x9cdryxe2x80x9d cleans.
There are two general types-of plasma dry cleaning processes. One type forms a plasma inside the processing chamber, or xe2x80x9cin situxe2x80x9d. An example of an in situ plasma clean uses fluorine-containing gases such as NF3, C2F6, or C3F8 to form free fluorine for removing residue in the chamber interior.
Another approach to cleaning is to form a plasma in a remote plasma generator and then flow the ions into the processing chamber. Such a remote plasma cleaning process offers several advantages, such as providing a dry clean capability to a deposition system that does not have an in situ plasma system. Furthermore, a remote plasma system may be more efficient at converting cleaning plasma precursor gases or vapors into a plasma, and forming the plasma outside the chamber protects the interior of the chamber from potentially undesirable by-products of the plasma formation process, such as plasma heating and sputtering effects.
There are, however, some less advantageous aspects associated with the utilization of remote plasmas. One issue is that the remotely generated plasma may recombine to form less reactive species as the ions are flowed to the chamber. Such unwanted recombination reduces the effective concentration of the ions that are available to react in the chamber.
FIG. 3A is a simplified schematic view of a conventional chemical vapor deposition (CVD) processing system 310. CVD processing system 310 includes walls 312 and lid 314 defining deposition chamber 316 housing substrate support 318. The substrate support member 318 is typically made of a ceramic or aluminum nitride (AIN) and may include a heater such as a resistive heating coil disposed inside the substrate support member, and may also include substrate chucking mechanisms for securely holding a substrate, such as a vacuum chuck or an electrostatic chuck.
Processing gas source 320 is in fluid communication with processing chamber 316 through mixing manifold 322 of gas delivery system 324. Mixing manifold 322 is also in fluid communication with remote plasma generator 326 featuring RF source 328 and gas source 330. Gas delivery system 324 further comprises gas box 332 in fluid communication with mixing manifold 322, blocker plate 334 in fluid communication with gas box 332, and gas distribution face plate 336 in fluid communication with blocker plate 334.
Vacuum exhaust system 338 is connected to a gas outlet or foreline 342 of the chamber 316. The exhaust system 338 includes one or more vacuum pumps 340, such as a turbomolecular pump, connected to exhaust gases from and maintain vacuum levels in the chamber 316. The one or more vacuum pumps 340 are connected to the foreline 342 for exhausting gases through a valve such as a gate valve. One or more cold traps 344 may be disposed on foreline 342 to remove or condense particular gases exhausted from the chamber.
FIG. 3B is a simplified cross-sectional view of the conventional gas distribution system shown in FIG. 3A. Gas distribution system 324 comprises mixing structure 322 configured to receive a flow of gas or remotely-generated plasma. Gas distribution system 324 also comprises gas box 332 having inlet 332a to center bore 332b that is configured to receive a flow of gases or ions from mixing structure 322. Blocker plate 334 having orifices 334a is affixed to the bottom of gas box 332.
Blocker plate 334 is a gas passageway which functions to transform the flow of gases through the relatively narrow conduit of the gas box into a homogenous gas flow over the entire expected surface area of the wafer positioned within the processing chamber. Accordingly, orifices 334a of blocker plate 334 are sized and positioned to create an initial, coarse distribution of flowed ions/gases over the expected substrate surface. Due to the configuration of holes in the blocker plate that are necessary to accomplish this initial coarse distribution, gases passing through the distribution system experience a pressure increase in region 399 immediately upstream of the blocker plate.
Ions or gases flowed through blocker plate 334 are in turn conveyed to gas distribution face plate 336 having orifices 336a. The orifices 336a of gas distribution face plate 336 are designed to accomplish a finer distribution of flowed gases/ions over the entire surface of the substrate, in order to ensure deposition of a layer of material of even thickness thereon. A larger number of orifices are thus typically present in the gas distribution faceplate than in the blocker plate. Because of the relatively large number of orifices in the faceplate, and because coarse distribution of gas flow has already been accomplished by the blocker plate, the increase in pressure upstream of the gas distribution face plate is relatively small compared with that arising upstream of the blocker plate.
Ions or gases flowed out of gas distribution face plate 336 enter the chamber and are available to participate in chemical reactions occurring therein, for example removal of residue formed on exposed surfaces of the chamber. However, ion recombination promoted by high pressure reduces the effective concentration of ions in the chamber and thus their cleaning effectiveness.
Therefore, there is a need in the art for methods and apparatuses which reduce the recombination of ions in a remotely-generated plasma that is flowed into a semiconductor fabrication chamber for processing.
A flow of a remotely-generated plasma to a processing chamber by-passes a blocker plate and thereby avoids unwanted recombination of active species. By-passing the blocker plate according to embodiments of the present invention avoids the high pressures arising upstream of the blocker plate, inhibiting ion recombination and elevating the concentration of reactive ions available in the processing chamber for cleaning and other reactions. In accordance with one embodiment of the present invention, the flowed ions may be distributed beyond the edge of an underlying blocker plate through channels of a separate by-pass plate structure positioned between the gas box and the blocker plate. In accordance with an alternative embodiment in accordance with the present invention, the flowed ion may be distributed beyond the edge of an underlying blocker plate through channels present in the gas box itself.
An embodiment in accordance with the present invention of a gas distribution system for a substrate processing chamber comprises a gas distribution faceplate having a first plurality of gas holes adapted to introduce a gas into the substrate processing chamber. A first gas inlet has a cross-sectional area smaller than the surface area of the substrate. A first gas passageway is fluidly coupled to the first gas inlet and to the first plurality of gas holes, the first gas passageway comprising a second plurality of gas holes configured to transform a flow of gas from the first gas inlet into a flow of gas having the cross-section of the surface area of the substrate. The gas distribution system further comprises a second gas inlet and a second gas passageway fluidly coupled to the second gas inlet and to the first plurality of gas holes, wherein the second gas passageway allows gases to flow from the second gas inlet to the first plurality of gas holes, while by-passing the second plurality of holes.
An embodiment of a gas distribution system in accordance with the present invention for a semiconductor fabrication chamber comprises a gas box having a first channel in fluid communication with a processing gas source and a second channel in fluid communication with a remote plasma source. A blocker plate defines a plurality of orifices in fluid communication with the first inlet of the gas box. A gas distribution faceplate defines a plurality of orifices in fluid communication with the orifices of the blocker plate and in fluid communication with a chamber of a processing tool. A by-pass plate is positioned between the gas box and the blocker plate, the by-pass plate having a first channel in fluid communication with the first channel of the gas box and with the blocker plate orifice, the by-pass plate including a second channel in fluid communication with the second gas box channel, the second channel of the by-pass plate in fluid communication with the chamber without passing through the blocker plate orifice.
Another embodiment of a gas distribution system in accordance with the present invention for a semiconductor fabrication chamber comprises, a gas box including a first channel including an outlet and an inlet in fluid communication with a processing gas source, and a second channel including an outlet and an inlet in fluid communication with a remote plasma source. A blocker plate defines a plurality of orifices in fluid communication with the first gas box channel outlet. A gas distribution faceplate defines a plurality of orifices in fluid communication with the orifices of the blocker plate and with the processing chamber.
An embodiment of a method in accordance with the present invention for distributing gas to a semiconductor processing chamber comprises, generating a flow of a processing gas and causing the flow of the processing as to move through an orifice in a blocker plate prior to entering the processing chamber. A flow of a plasma is generated remote from the processing chamber. A flow of remote plasma is caused to by-pass the orifices in the blocker plate before entering the processing chamber.
An embodiment of a method in accordance with the present invention for enhancing a cleaning effectiveness of a plasma generated remote from a processing chamber comprises, causing a flow of the remotely-generated plasma to by-pass a high pressure region upstream of a blocker plate before entering the processing chamber.
A further understanding of embodiments in accordance with the present invention can be made by way of reference to the ensuing detailed description taken in conjunction with the accompanying drawings.